It is a fair point, but in my mind Anderson Silva is a living legend in the sport and makes the grade in both massive PPV buys and legacy standing.
I have a hard time disqualifying him from being in a 'superfight' because he is no longer champion. When he fought Forrest it was considered a superfight despite coming off a summary TKO loss to Rashad.
Generally I think of a superfight in terms of two marquee fighters from different divisions being booked. Two marquee fighters who would otherwise not meet unless one or both moved weight, thus, making it a 'superfight' as opposed to something that would happen in the course of divisional rankings insisting the fight happen.